Interchain Spacing Research Articles

Incorporating hydrogen bonding networks in microporous polymer membranes for high-flux hydrocarbon separation

Polymer membranes have been most commonly utilized in gas separations, while they often suffer from the trade-off between membrane permeability and selectivity, which arises from the inherent coupling between polymer chain rigidity and interchain spacing. Here, we propose a hydrogen bonding network strategy, where hydrogen bonding acceptors are incorporated into amidoxime-functionalized polymer of intrinsic microporosity (AO-PIM) membranes to in situ construct hydrogen bonding networks with amidoxime groups, and to modulate the interchain spacing/micropore structure in AO-PIM. Especially, 2,2′-bipyridine endows AO-PIM membranes with appropriate match between polymer chain rigidity and interchain spacing, leading to dramatically enhanced C3H6 permeability of 262 Barrer, 2.9 times higher than AO-PIM membranes, with a C3H6/C3H8 selectivity of 24 under mixed-gas tests, surpassing all the reported polymer membranes and most mixed matrix membranes. We envision this scalable, generic hydrogen bonding network strategy opens an alternative avenue for polymer membranes to break the trade-off effect.

Interplay of bipyridine and 4,4′-diaminodiphenylmethane ligands in crystal design of cadmium-based coordination polymers: Structures and unusual photoluminescence quenching

Starting from Cd(ClO4)2·2H2O, four positively charged coordination polymers were prepared and characterized by IR spectroscopic and single-crystal X-ray diffraction methods. The obtained crystalline solids included one-dimensional coordination polymers, {[Cd(dadpm)(2,2′-bpy)2](ClO4)2}n (1), and {[Cd(dadpm)(2,2′-bpy)2](ClO4)2·0.5(H2O)}n (2), and two-dimensional coordination polymers, {[Cd(4,4′-bpy)2(H2O)2](ClO4)2(dadpm)2}n (3), and {[Cd(4,4′-bpy)2(H2O)2](ClO4)2(4,4′-bpy)0.5(dadpm)·EtOH}n (4) (dadpm = 4,4′-diaminodiphenylmethane, 2,2′-bpy = 2,2′-bipyridine; 4,4′-bpy = 4,4′-bipyridine). The similar one-dimensional coordination backbones in 1 and 2 were originated from the mononuclear Cd(II) coordination cores with the N6 distorted octahedral geometries going from two terminal bidentate-chelate 2,2′-bpy and two bidentate-bridging dadpm ligands that mediated the successive metal atoms in coordination chains. The charge-balanced perchlorate anions were located in the interchain space complemented by water molecules in 2. The coordination chains were interconnected into H-bonded networks via NH(NH2)⋯O hydrogen bonds. The 2D coordination polymers 3 and 4 comprised the same positively charged square-grid infinite networks {[Cd(4,4′-bpy)2(H2O)2]2+}n with sql topology and with cadmium atom in the N4O2 tetragonally distorted octahedral coordination geometry as a single node. The charge-compensated ClO4− anions and the dadpm molecules were located in the interlayer space in 3 being complemented by the 4,4′-bpy and EtOH molecules in 4. The solid-state photoluminescence in all reported coordination polymers was significantly attenuated and redistributed along the spectrum in comparison with the pure dadpm which revealed the dual emission in the form of a strong narrow signal in the ultraviolet and a weak signal in the yellow regions of spectrum.

Manipulating Cis-Trans Copolymer Chain Conformation to Simultaneously Improve Permittivity and DC Breakdown Strength in Polythiourea.

Polythioureas (PTUs) show great potentials for applications in the new generation of film capacitors due to their excellent dielectric properties. Herein, the cis-trans copolymer chain of PTU is successfully tailored by employing cis and trans cyclohexyl spacers. The relationship between the copolymer chain conformation, microstructure, and dielectric properties is carefully explored by a series of analysis. Compared with cis conformation, the trans with less steric hindrance can promote the formation of H-bonds. The enhanced H-bonding interactions not only reduce the molecular inter-chain spacing, but also drive the self-assembly of molecular chains to form cylindrical and droplet nano-morphologies. The phase separation between cis and trans PTUs is confirmed by combining the experimental results of TEM and DSC, and the CT64-PTU with the most two-phase interface thus obtains the highest permittivity of 5.5 (@10Hz). The reduced molecular inter-chain spacing is accompanied by a decreased hopping distance of charges, which improves breakdown strength by 17% from 498 MV/m to 580 MV/m. Therefore, the cis-trans copolymer chain conformation in PTU provides a simultaneous high permittivity and breakdown strength. This research offers a strategy to further design high-performance dielectrics via regulation of copolymer chain conformation.

VS4/MoS2 cathodes with long cycle life and high rate performance for hybrid magnesium-lithium batteries

Hybrid magnesium-lithium batteries (MLIBs) have become the focus of research due to the advantages of combining a magnesium metal anode (free dendrite) and Li-driven reaction cathode (fast ion diffusion rate). VS4 with large interchain space can be used as a potential cathode for MLIBs, but its low conductivity and weak structural stability limit the development of MLIBs. In this work, MoS2 was introduced into VS4 to induce the generation of abundant sulfur vacancies, which improved the structural stability and Li+ ion transport properties of VS4. The VS4/MoS2 cathode retains stability and an impressively high reversible capacity of 581.7 mAh·g−1 after 100 cycles, corresponding to a capacity retention of 98.99 % (compared with the second cycle). Meanwhile VS4/MoS2 still has 472.64 mAh·g−1 at high current density of 1500 mA·g−1, which is much higher than that of NF-VS4 (11.9 mAh·g−1) and VF-VS4 (29.8 mAh·g−1). This work points the way to ameliorate Mg-based rechargeable batteries.

Study on synergy effect of hydrated ionic radius and oxidation state for pre-intercalated cations towards highly reversible magnesium ions batteries

Magnesium ions batteries (MIBs) are promising in that Mg anode shows high theoretical volumetric capacity (3833 mAh cm−3) and is dendrite free deposition upon charging. However, the higher charge/radius ratio of Mg2+ with bivalent nature shows strong electrostatic interaction between Mg2+ and host anion lattice of VS4in situ grown on N doped tubular graphene (VS4/N-TG), causing the sluggish reaction kinetics and poorer structural stability. Therefore, there is great need to develop strategy for modifying VS4/N-TG. Although interlayer pre-intercalation is an effective way to improve the overall cell performance, the systematic study about the various ionic radius and oxidation states of pre-intercalated cations on modulating electronic structure to enhance the electrochemical performance has not been focused. In this study, cations pre-intercalation engineering is achieved in VS4/N-TG for constructing M0.06VS4/N-TG cathode via electrochemical method. After the systematic study about the effect of hydrated ionic radius and oxidation state of various pre-intercalated cations on electrochemical performance of M0.06VS4/N-TG, pre-intercalated Mg2+ with moderate hydrated ionic radius and oxidation state would enlarge the interchain spacing for facilitating magnesium working ions transportation and maintaining structural stability, as well as change the oxidation states of V element as V2+ and V3+ to enhance the electrochemical reactivity. Therefore, Mg0.06VS4/N-TG deliver superior electrochemical properties, including the excellent cycling stability with nearly 100% capacity retention ratio after 1500 cycles, high specific capacity about 170 mAh/g at 50 mA g−1, superior rate capability (107 mAh/g at 1000 mA g−1) and high anti-self-discharge behavior. The highlighted synergic effect of the hydrated ionic radius and oxidation state would guide more energy storage devices design for obtaining the excellent electrochemical performance.

Facile in situ synthesis of 1D VS4 membrane for efficient nanofiltration

The framework dimension has been proven to exert significant influence on the separation performance of molecular sieve membranes (MSMs). Compared with the flourishing research on three-dimensional (3D) and two-dimensional (2D) membranes, relevant studies on one-dimensional (1D) membranes remained rarely explored to date. In this study, well-intergrown 1D VS4 membranes were facilely prepared by in situ solvothermal growth. Among various synthetic parameters, the pH value of the precursor solution was found to play a crucial role in modulating the membrane microstructure, so that uniform and continuous 1D VS4 membrane could be obtained at the pH value of 10 in ethylene glycol-H2O (EG-H2O) binary solvent. Relying on regular interchain space and great hydrophilicity, our membrane displayed excellent dye rejection efficiency (>99.0%), thus holding great promise for energy-efficient separation.

Novel microporous sulfonated polyimide membranes with high energy efficiency under low ion exchange capacity for all vanadium flow battery

High proton conductivity and low vanadium permeation created great challenges in designing of highly efficient membranes for all vanadium redox flow battery. To overcome this trade-off phenomenon, a series of novel microporous sulfonated polyimides (SPI) with gradient sulfonic acid group concentrations (6FTMA-X) were prepared by a simple one-step polymerization. They demonstrated high molecular weight (Mn of 23 to 59 KDa), modest microporosity (SBET = 437.2 - 39.4 m2 g−1) and suitable interchain space (between 3.7 and 5.2 Å), which provided excellent ion sieving for proton and vanadium ions (2.4 and 6.0 Å). Consequently, although the ion exchange capacities (0.38 - 1.47 mmol g−1) of 6FTMA-Xs were low compared with the reported SPIs, they still achieved high energy efficiency (80.4%) under high current density (100 mA cm−2), which was comparable to Nafion 117 (N117, 81.7%) at the same current density. This was because of the acceptable proton conductivity and ultra-low vanadium permeation (0.59 - 3.56 × 10−7 cm2 min−1). We suppose the micropore inside the sulfonated polyimides behaviors as ion channel for proton transport and a vanadium barrier. All these results demonstrate that the 6FTMA-X membranes show great potential for vanadium redox flow battery applications. This polymer design strategy provided new insight for highly efficient membranes for VRFB applications.

Sequential Separation of Linear, Mono-, and Di-Branched Hexane Isomers on a Robust Coordination Polymer with Nonbonding Flexibility.

Efficient separation of hexane isomers is a crucial process for upgrading gasoline. Herein, the sequential separation of linear, mono-, and di-branched hexane isomers by a robust stacked 1D coordination polymer termed as Mn-dhbq([Mn(dhbq)(H2 O)2 ],H2 dhbq = 2,5-dihydroxy-1,4-benzoquinone)is reported. The interchain space of the activated polymer is of optimal aperture size (5.58 Å) that could exclude 2,3-dimethylbutane, while the chain structure can discriminate n-hexane with high capacity (1.53mmol g-1 at 393 K, 6.67kPa) by high-density open metal sites (5.18mmol g-1 ). With the temperature- and adsorbate-dependent swelling of interchain spaces, the affinity between 3-methylpentane and Mn-dhbq can be deliberately controlled from sorption to exclusion, and thus a complete separation of ternary mixture can be achieved. Column breakthrough experiments confirm the excellent separation performance of Mn-dhbq. The ultrahigh stability and easy scalability further highlight the application prospect of Mn-dhbq for separation of hexane isomers.

Polyimide Nanodielectrics Doped with Ultralow Content of MgO Nanoparticles for High-Temperature Energy Storage.

Advanced polymer dielectrics with high energy density at elevated temperatures are highly desired to meet the requirements of modern electronic and electrical systems under harsh conditions. Herein, we report a novel polyimide/magnesium oxide (PI/MgO) nanodielectric that exhibits high energy storage density (Ue) and charge–discharge efficiency (η) along with excellent cycling stability at elevated temperatures. Benefiting from the large bandgap of MgO and the extended interchain spacing of PI, the composite films can simultaneously achieve high dielectric constant and high breakdown strength, leading to enhanced energy storage density. The nanocomposite film doped with 0.1 vol% MgO can achieve a maximum Ue of 2.6 J cm−3 and a η of 89% at 450 MV m−1 and 150 °C, which is three times that of the PI film under the same conditions. In addition, embedding ultralow content of inorganic fillers can avoid aggregation and facilitate its large-scale production. This work may provide a new paradigm for exploring polymer nanocomposites with excellent energy storage performance at high temperatures and under a high electric field.

Unlocking the Carbyne-Enriched Nanocoating Sensitivity to Volatile Organic Vapors with Plasma-Driven Deposition onto Bulk Micromachined Silicon Membranes.

Due to the unique combination of physicochemical and structural properties of carbyne-enriched nanocoatings, they can be used for the development of high-end electronic devices. We propose using it for the development of sensor platforms based on silicon bulk micromachined membranes that serve as a part of microcapacitors with flexible electrodes, with various sizes and topologies. The carbyne-enriched nanocoating was grown using the ion-assisted pulse-plasma deposition method in the form of 2D-ordered linear-chain carbon with interchain spacing in the range of approximately 4.8–5.03 Å. The main characteristics of the fabricated sensors, such as dynamic range, sensitivity, linearity, response, and recovery times, were measured as a function of the ethanol concentration and compared for the different sizes of the micromembranes and for the different surface states, such as patterned and non-patterned. The obtained results are the first step in the further optimization of these sensor platforms to reach more precise detection of volatile organic compounds for the needs of the healthcare, air monitoring, and other relevant fields of human health.

Gas-Sensing Properties of a Carbyne-Enriched Nanocoating Deposited onto Surface Acoustic Wave Composite Substrates with Various Electrode Topologies

The application of carbyne-enriched nanomaterials opens unique possibilities for enhancing the functional properties of several nanomaterials and unlocking their full potential for practical applications in high-end devices. We studied the ethanol-vapor-sensing performance of a carbyne-enriched nanocoating deposited onto surface acoustic wave (SAW) composite substrates with various electrode topologies. The carbyne-enriched nanocoating was grown using the ion-assisted pulse-plasma deposition technique. Such carbon nanostructured metamaterials were named 2D-ordered linear-chain carbon, where they represented a two-dimensionally packed hexagonal array of carbon chains held by the van der Waals forces, with the interchain spacing approximately being between 4.8 and 5.03 Å. The main characteristics of the sensing device, such as dynamic range, linearity, sensitivity, and response and recovery times, were measured as a function of the ethanol concentration. To the authors’ knowledge, this was the first time demonstration of the detection ability of carbyne-enriched material to ethanol vapors. The results may pave the path for optimization of these sensor architectures for the precise detection of volatile organic compounds, with applications in the fields of medicine, healthcare, and air composition monitoring.

Materials Design of Highly Branched Bottlebrush Polymers at the Intersection of Modeling, Synthesis, Processing, and Characterization

Highly branched “bottlebrush” polymers are a class of macromolecules characterized by side chains that are densely grafted from a backbone that is typically linear. Their unique and often-desirable properties stem from steric repulsion between side chains, which stiffens the molecular contour and increases interchain spacing. There has been a renaissance in both our fundamental understanding, practical synthesis, and application of these materials, due to synergistic advances in all branches of polymer science. In this perspective, we outline how a wide variety of new functional bottlebrush materials have emerged from the convergence of insights from the entire materials design process; the integration of synthesis, characterization, processing, and modeling has demonstrated the promise of these branched macromolecules as a versatile platform for molecular engineering. We discuss how this platform may be further developed to exhibit novel material properties in and out of equilibrium and put into practice due to the next generation of synthetic, analytical, processing, and computational tools in materials chemistry.

Tröger’s Base Polyimide Hybrid Membranes by Incorporating UiO-66-NH2 Nanoparticles for Gas Separation

Hybrid membranes based on the Tröger’s base polyimide (PI-TB) as a rigid microporous polymer matrix containing a kinked N-heterocycle and a kind of CO2-philic porous UiO-66-NH2 nano-filler were successfully fabricated for gas separation. This new hybrid membrane exhibits good interfacial compatibility through hydrogen bonds and charge transfer interactions between the PI-TB matrix and the UiO-66-NH2 nano-filler, thus enabling a relatively high loading and well dispersion of nano-filler. Meanwhile, the as-synthesized UiO-66-NH2 nanoparticles increase the average inter-chain spacing distance of PI-TB by interfering with the packing of polymer chains and thus providing additional transport pathways in the membranes. The pure gas permeabilities and ideal selectivities for CO2/CH4, CO2/N2, and O2/N2 systems were investigated at 35 °C and a feed pressure of 1 bar. Among them, the hybrid membrane containing 30 wt % UiO-66-NH2 exhibits the optimal gas separation performance with enhanced permeabilities of CO2 and O2 increased by ∼166% (415 and 92.3 Barrer, respectively) while maintaining comparable CO2/CH4, CO2/N2, and O2/N2 gas pair selectivities (25.0, 18.9, and 4.2, respectively) with the pristine PI-TB membrane. This work enriched the studies on the post-modification of PI-TB as a potential candidate membrane material for gas separation.

PVP-induced synergistic engineering of interlayer, self-doping, active surface and vacancies in VS4 for enhancing magnesium ions storage and durability

Magnesium ions batteries (MIBs) provide great potential for the safety and large-scale energy storage, however, its inherent drawbacks, such as the sluggish kinetics, poor cycling life and lower specific capacities of cathode limit their practical application. Herein, PVP is innovatively incorporated with VS4 and induced synergistic engineering, including the enlarged interchain spacing, V3+ self-doping, rich sulfur vacancies and the selectively exposing active surface of (020) facets, which results in the fast kinetics of co-intercalation of Mg2+ and MgCl+, electrolyte infiltration, more active sites exposure, and the strain/stress relaxation during insertion/extraction process for the high stability of structure. Therefore, this novel design of PVP-VS4 exhibits long-term cycling stability (80% capacity retention at 5000 mA g−1 after 1500 cycles) and exceptional high-rate capability (140 mAh g−1 at 50 mA g−1 with 45 mAh g−1 at 5000 mA g−1). The fast reaction kinetics is further confirmed by galvanostatic intermittent titration technique (GITT) and density functional theory (DFT) computations. In addition, the energy storage mechanism and desirable pseudocapacitive behaviors are elucidated through series of ex situ investigations and pesudocapaticance-like contribution analysis. And PVP-VS4 delivers the higher anti-self-discharge capability cause by PVP incorporation. PVP-induced synergistic engineering opens up a new opportunity for designing a variety of effective intercalation host materials for next-generation energy storage.

High-temperature energy storage performances of “isomer-like” polyimide and its thermoplastic polyurethane blending system

The interchain space of polyimide is optimized to hinder charge carrier transport, thus improving the energy storage performance at high temperatures.

Structures and properties of polyimide fibers prepared via gel spinning induced by chemical imidization

A series of 3,3′,4,4′-biphenyldianhydride (BPDA)/p-phenylene diamine (PDA) polyimide (PI) fibers were prepared through a novel gel spinning method induced by chemical imidization. The effects of draft ratios, solvent content and thermal treatment temperature on the aggregation structure and properties of PI fibers in the gel spinning were systematically investigated by experiment and molecular dynamics (MD) simulation. The mechanical properties of the fibers are significantly improved with increasing draft ratio due to the development of the molecular orientation along the fiber direction during large-ratio drafting process. The MD simulation results indicate that the nascent gel fiber with more solvent content has larger interchain space and weaker interchain interaction and molecular chains tend to be arranged along the drafting direction. The highly oriented PI fibers are completely imidized after thermal treatment at 320 °C, reaching the optimum tensile strength of 1.43 GPa and modulus of 121 GPa. The surface and internal defects of the highly oriented PI fiber gradually increased with increasing the thermal treatment temperature, resulting in a slight decrease in mechanical properties. In a word, the fiber orientation is carried out before the thermal imidization in the gel spinning process, which can greatly increase fiber draft ratio and reduce the subsequent thermal treatment temperature and energy consumption.

Exploring Cation-Anion Redox Processes in One-Dimensional Linear Chain Vanadium Tetrasulfide Rechargeable Magnesium Ion Cathodes.

For magnesium ion batteries (MIBs) to be used commercially, new cathodes must be developed that show stable reversible Mg intercalation. VS4 is one such promising material, with vanadium and disulfide anions [S2]2- forming one-dimensional linear chains, with a large interchain spacing (5.83 Å) enabling reversible Mg insertion. However, little is known about the details of the redox processes and structural transformations that occur upon Mg intercalation and deintercalation. Here, employing a suite of local structure characterization methods including X-ray photoelectron spectroscopy (XPS), V and S X-ray absorption near-edge spectroscopy (XANES), and 51V Hahn echo and magic-angle turning with phase-adjusted sideband separation (MATPASS) NMR, we show that the reaction proceeds via internal electron transfer from V4+ to [S2]2-, resulting in the simultaneous and coupled oxidation of V4+ to V5+ and reduction of [S2]2- to S2-. We report the formation of a previously unknown intermediate in the Mg-V-S compositional space, Mg3V2S8, comprising [VS4]3- tetrahedral units, identified by using density functional theory coupled with an evolutionary structure-predicting algorithm. The structure is verified experimentally via X-ray pair distribution function analysis. The voltage associated with the competing conversion reaction to form MgS plus V metal directly is similar to that of intermediate formation, resulting in two competing reaction pathways. Partial reversibility is seen to re-form the V5+ and S2- containing intermediate on charging instead of VS4. This work showcases the possibility of developing a family of transition metal polychalcogenides functioning via coupled cationic-anionic redox processes as a potential way of achieving higher capacities for MIBs.

Rigid crosslinkers towards constructing highly-efficient ion transport channels in anion exchange membranes

Synthetic anion exchange membranes (AEMs) usually suffer from low conductivity, bad alkaline stability and poor dimensional stability. Constructing efficient ion transport channels is considered to be one of the most effective ways for preparing the AEMs with the high conductivity and low swelling ratio. Herein we demonstrate a facile strategy to achieve this goal via using the rigid crosslinkers to expend the interchain spacing of polymer chains. Three crosslinkers are chose to modify poly (ether ketone) (PEK) AEMs. The AEMs with rigid crosslinkers have more efficient ion transport channels and thus show both higher water uptake and higher ionic conductivity, compared with the AEM with the flexible crosslinker. Especially, the hydroxide conductivity of the AEM increases from 63.2 to 110.3 mS cm−1 at 80 °C when the short flexible crosslinker is replaced by the long rigid crosslinker. Meanwhile, the swelling ratios (SR) are less than 25%. The rigid crosslinkers should be beneficial to construct efficient ion channel and overcome the trade-off relation between the ionic conductivity and dimensional stability of the synthetic AEMs.

Interchain Spacing and Screening Length Modification of PSS Backbone Chains in Zwitterion-Doped Poly(3,4-Ethylenedioxythiophene):Polystyrene Sulfonate

The interchain spacing and screening length modification of deuterated PSS (d-PSS) backbone chains in zwitterion-doped PEDOT:d-PSS were studied as a function of the doping concentration using small angle neutron scattering. Results suggest that the dopant, 3-(N,N-Dimethylmyristylammonio)propanesulfonate (DYMAP), forms worm-like micelle structures in the PEDOT:d-PSS dispersion that grow in size as the doping concentration increases. The interchain spacing between negatively charged d-PSS remains unaffected by DYMAP up to 15 mM doping concentration. However, from 15 to 25 mM doping concentration, the interchain spacing increases due to steric interactions of grown DYMAP worm-like micelles with the d-PSS chains. At 30 mM doping concentration, the interchain distance between negatively charged d-PSS chains is reduced due to the gelation of the PEDOT:d-PSS dispersion caused by the crosslinking between long DYMAP worm-like micelles and d-PSS chains. Meanwhile, the screening length of the neutralized d-PSS segments attached to the PEDOT oligomers increases as the DYMAP concentration increases form 5 to 30 mM due to the neutralization of the negatively charged d-PSS segments by their Coulomb interaction with the cation in DYMAP.

Design of interchain hydrogen bond in polyimide membrane for improved gas selectivity and membrane stability

Polyimide has been widely investigated as a potential material for gas separation. The post-crosslinking of polyimide could increase gas selectivity and membrane stability due to increase of chain-packing density and chain stiffness. However, common crosslinking strategies tend to destroy the chemical structure of polyimide. In this work, a strong hydrogen bond among polymer chains of 6FDA-durene polyimide (Du-PI) membranes is designed by introducing isophthalic dihydrazide (IPD) molecules as cross-linker. The formation of hydrogen bond between Du-PI and IPD strengthens the polymer interchain interaction and regulates interchain spacing but without breaking the chemical structure of Du-PI. The resulting IPD/Du-PI membranes exhibit largely enhanced mechanical strength and anti-plasticization property in comparison with pristine Du-PI membranes. In addition, due to the increased packing density of polymer chains, the membranes show obviously increased gas perm-selectivity by 296%, 505%, 125%, 66%, and 171% for H2/N2, H2/CH4, H2/CO2, O2/N2, and CO2/CH4 gas pair in the case of 20% IPD/Du-PI membrane. The use of IPD as cross-linker has demonstrated herein to be a facile and effective strategy to strengthen the inter-polymer chain interaction and simultaneously improve membrane stability in a mild way.